1. Field of the Invention
The present invention relates to valves. More particularly, the present invention relates to actuated gate valves.
2. Description of Related Art
Gate valves are used to stop the flow of fluid in a tube or pipe. Typically, gate valves can handle material similar to the viscosity of water, or higher, as well as material that is in a vacuum or under small levels of pressure.
An exemplary prior art gate valve 100 is depicted in FIG. 1. An activation device 105, such as a pneumatic valve, is attached to the back side of a valve assembly frame 110 and transmits opening and closing forces to a valve plate 115, located on the front side of the valve assembly frame 110, using an actuator rod 125 coupled to a link 120 connected to an intermediate stem 155. A sealed housing 135 encloses the valve plate 115, and includes a coupling 130 through which the intermediate stem 155 passes. A piping interface plate 140, located on the front side of the housing 135, connects to a piping system (not shown), while another piping interface plate 142, located on the back side of the housing 135, attaches the housing 135 to the valve assembly frame 110. The piping interface plate 141 is coupled to the piping system (not shown) through an opening in the valve assembly frame 110. An additional piping interface plate (not shown) may also be attached to the back side of the valve assembly frame 110.
If the link 120 is connected directly to the intermediate stem 155 (not shown), an undesirable torque is applied to the intermediate stem 155 due to the misalignment of the line of action of the force applied by the activation device 105 and the centerline of the intermediate stern 155. This torque produces undesirable stresses in the intermediate stern 155 and the valve plate 115, as well as misalignments among the various components.
In order to reduce the effects of these undesirable stresses and misalignments, a spring assembly 150 can be incorporated into the gate valve 100 (shown), The spring assembly 150 includes upper and lower nuts 152, 154, attached to the intermediate stem 155, and upper and lower springs 156, 158, acting between the upper and lower surfaces of the link 120 and the upper and lower nuts 152, 154, respectively. Forces applied by the link 120 to the spring assembly 150 are transmitted to the intermediate stem 155 through the upper and lower nuts 152, 154, while misalignment of the Intermediate stern 155 is reduced due to the transverse flexibility of the spring assembly 150 and the freedom of movement afforded by the simple, contact interfaces between the upper and lower surfaces of the link 120 and the upper and lower springs 156, 158, respectively, as well as between the upper and lower springs 156, 158, the upper and lower nuts 152, 154, respectively.
However, the prior art gate valve 100 is mechanically complex, the undesirable stresses and misalignments have not been entirely eliminated and the upper and lower springs 156, 158 can limit the force that can be applied by the activation device 105 to the valve plate 115, resulting in unsatisfactory performance in many situations. Therefore, there is a need for an actuated gate valve that does not suffer from these infirmities.